This is the largest of the research cores, consisting of nine investigators working on various aspects of mutagenesis and carcinogenesis. It brings together toxicologists, molecular biologists, epidemiologist and geneticists. The multi-disciplinary projects range in scope from studies on DNA damage through human population studies on biomarkers and cancer risk. The core leader is Dr. Allan Smith. Accomplishments from his laboratory include evidence for genotoxic effects in exfoliated bladder epithelial cells in human population exposed to arsenic in drinking water. Other accomplishments of this core include findings by Dr. Ames that oxidative DNA damage plays a major role in aging and cancer, that mitochondria are an important source of these oxidants, and that dietary antioxidant can protect against oxidative damage in humans. New Salmonella tester strains (Ames II test) have also been developed. New fluorescent labels for analysis of nucleic acid have been developed by Dr. Alexander Glazer. Dr. Lois Gold, in collaboration with Dr. Bruce Ames, has developed ranking schemes and databases for carcinogenic agents to which humans are exposed. Dr. Alexander Karu has developed immunoassays to detect PCBs and PAHs. Dr. Stuart Linn has added to our knowledge of the steps involved in oxidative DNA damage. Dr. Martyn Smith has new findings on the genotoxic effects of benzene metabolites, as well as development of a FISH technique for micronuclei in exfoliated bladder experiments which was used in the studies of Dr. Allan Smith.